KR940010232B1 - Prcess & device for inspecting control rod clusters for nuclear fuel assemblies - Google Patents

Abstract

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Description

Test method and device for control rod cluster for nuclear fuel assembly

1 is a top perspective view of a conventional control rod cluster used in a pressurized water reactor.

2 shows a simplified partial cross-sectional view of a fuel building for a nuclear power plant, in which a device according to the invention can be installed.

3 is a schematic top elevation view of a test device fitted with a deflection vane having a function of guiding a process gripper during downward motion.

4 is a block diagram of a top schematic view of a device according to an embodiment of the present invention and associated components (deflector, ultrasonic instrument and its electronic device not shown).

5 is a side view of the upper support plate and the top of the body of the device shown in FIG.

FIG. 6 is a cross-sectional view of the upper support plate and positioning plate and the top of the device shown in FIG. 4 along the VI-VI plane of FIG.

7 is a top view of the positioning plate and the upper support plate viewed from the surface directly above the vortex current coil.

8 illustrates an embodiment of a removable vertical offset block for a test apparatus.

9 is a view from above of part of the removable block of FIG. 8;

10 is a top view showing a first support at the top of the device body and a second support at the bottom.

11 is a cross-sectional view taken along line XI-XI of FIG. 7 showing how the visual inspection mirror is fixed.

12 is a left side view of FIG.

13 is a schematic cross-sectional view of the structure of a remote control control panel carrying a rotating ultrasonic sensor along a vertical plane;

14 is a cross-sectional view taken along the line XIV-XIV in FIG.

* Explanation of symbols for main parts of the drawings

10: control rod cluster 12: control rod

14: inspection device 16: fuel building

24: fuel assembly 30: upper support

32: body 34: vertical offset block

35: data processor 36: TV monitor

37: video tape recorder 39: legs

42: video camera 44: stand

46: vortex current coil 50: horizontal table

72: guide 78: crossbar

86: pedestal 88: indexing lug

92 mirror holder 94 strip

100,130: mirror 106: ultrasonic inspection unit

108: electric motor 116: flexible coupling

120: support 122: guide member

[Background of invention]

The present invention relates to the inspection of control rods constituting a cluster that can be inserted into the core of a nuclear reactor. In particular, all control rods are used to measure the wear of the control rods and then complete the first test by visual inspection or by another method. The present invention relates to a test method and an apparatus for enabling a first test of the same.

[Private Technology]

The present invention is suitably used to inspect control rods of control rod clusters that can be inserted into fuel assemblies for light water cooling and deceleration reactors. In such a reactor, control rod clusters each having neutron absorbing rod bundles are used, each bundle having twenty-four control rods carried by the arm of the upper processing member, commonly referred to as spiders, for example. Some of the control rod clusters are intended to control fine reactions while the reactor is in normal operation, and in particular can change the thermal power. Other clusters contain flammable poisons and are introduced into the core during the first cycle of the core. In other groups, the control rods may simply constitute plugs having the function of closing the guide tube provided to the fuel assemblies and suggesting coolant flow therein.

Control rods should be checked as periodically as possible to detect surface defects. Particularly in clusters where the degree of insertion in the core is often modified, it is desirable to verify the amount of wear to sufficiently and early measure the risk of sheath breakage and its contamination. This monitoring task is particularly useful when the power plant is used in a "load follower" mode of operation that requires frequent modifications to the degree of insertion of groups in the core.

French Patent No. 2,298,859 discloses an inspection method and apparatus for inspecting fuel rods in a reactor rather than checking control rod clusters. The rods are moved longitudinally relative to the inspection unit carrying the measurement signal. The inspection unit has a yoke with a prism endoscope and a sensor for measuring the distance between the outer diameter of the rod and the adjacent rods.

Such attempts are subject to serious limitations. If cracks are already present, only the visual test of the bar surface can be measured. An evaluation review of the future risk of such a crack was not provided. Sensors were used to measure the diameter of only one cross section. It was not possible to prepare a map showing the distribution of wear along the entire length of the rod or to provide an indication of layer wear.

Overview of the Invention

It is an object of the present invention to provide an improved inspection method in the form described above. In particular, it is an object of the present invention to provide a method that can detect a rod that is likely to be in a critical state and then apply the first inspection step to all the rods of the cluster to complete the diagnosis for that rod only in the second stage. . In this sense, the present invention provides a versatile inspection method that enables irradiation to be completed only for rods that have been shown to present a risk of breakage from the first experimental step.

According to the invention, (a) the control rod cluster having a plurality of n control rods is moved longitudinally through the control unit while the vortex current test is applied simultaneously to n / m control rods (n and m are predetermined integers) and (b) repeat step (a) m-1 times after the cluster has been rotated by a continuous amount of 360 ° C./m around the longitudinal direction, and (c) the suspicious control rod shown during steps (a) and (b) To provide a detailed map of the suspicious area, ultrasonically inspecting one over the entire axial length of the suspicious area and one after the other along the longitudinal direction of each suspicious control rod. An inspection method is provided.

Often, it would be advantageous to adopt m = 4 if the cluster is intended for use in a fuel assembly having a rotationally symmetric rectangular cross section. In particular, if such a selection is made, inspection of clusters containing 24 control rods frequently used in pressurized water reactors (PWRs) may be performed with only six vortex current coils. The coils may then be easily installed in the inspection unit.

If necessary, the test method may be terminated by completing a visual test with the camera once over the entire perimeter of the suspicious control rod while the control rod is reciprocated vertically. In particular, by using mirrors placed behind the control rods to engage the camera, the front of the control rod can be inspected while the control rod cluster is descending, and the back of the control rod can be inspected while the cluster is raised.

Visual or ultrasonic tests can be performed on suspicious control rods that were diagnosed during the previous vortex current test while vortex current tests were performed on another set of n / m control rods.

The invention will be better understood from the following description with reference to the accompanying drawings of specific embodiments given by way of example.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inspection apparatus described by way of example is suitable for testing a control rod cluster of a nuclear reactor with a fuel assembly having fuel rods distributed at nodes in a rectangular arrangement. Referring to FIG. 1, the control rod cluster 10 has 24 neutron absorbing rods, that is, the control rod 12, carried by the spider 13. These rods are sized to slide along the guide tubes in the guide tubes distributed at some of the 17 x 17 nodes of the fuel rod arrangement in the assembly. Each control rod 12 has a bullet-shaped conical end that is easily inserted into an associated guide tube.

Typically, the inspection device 14 is placed in a fuel building 16 installed adjacent to a reactor containment vessel (not shown) and communicates with the containment vessel via a fixed chamber 18. The fixed chamber is opened into a pool for receiving the inspection device 14. A processor 22 capable of gripping the entire fuel assembly 24 is provided to bring the assembly to the reservoir 26. The processor 22 has a cluster processing tool for removing the cluster contained in the fuel assembly and inserting it into the inspection apparatus 14.

The inspection device 14 may constitute an independent unit that can be processed by a processor. With reference to FIG. 3, an upper end thereof may be provided with a deflection vane made of curved metal which indexes the center of the gripper at the bottom of the clustering tool. The device may also have an illumination lamp in a sealed container for construction in the pool. If an inspection task is to be performed, the entire inspection device 14 is placed in a machine for immersion at a controllable depth in the pool. In particular, the device may be arranged in a basket of the lifting device 15, which is generally provided in a storage pool.

Nuclear fuel assemblies and components for processing the inspection device 14 and cluster 10 are omitted since they are conventional. With regard to processing tools, reference may be made to European Patent Application No. 84,402,050, published as 138,711.

Referring to FIG. 4, the inspection device 14 includes an upper support 30 (FIGS. 5-7) defining a test area, a body 32 supporting a vertical guide tube 72 for the control rods of the cluster. (FIGS. 5 and 6), removable spacers or vertical offset blocks 34 to place the device in the fuel reservoir at a height such that the support is placed on top of the reservoir, and each of eight Horizontal table 50 which can be controlled manually (FIGS. 6 and 7) or remotely controlled (FIG. 13) to bring the ultrasonic sensor or camera to the test area at eight inspection sites associated with the control rod position. Can be considered to have.

The apparatus also includes a data processor 35 and a display unit installed outside the pool, the function of which is to process the vortex current and the ultrasonic signals. In addition, the apparatus comprises a video monitor 36 and, if desired, a video tape recorder 37 associated with the video camera 42 which generally constitutes a visual inspection unit.

[Upper support]

5 to 7, the upper support consists of four legs 39 of triangular cross section installed in the four corners of a square plate having the same cross-sectional area as the fuel assembly. A hole 41 is provided through each leg 39. For each angular position of the cluster processing tool, two centering and indexing fingers 27 (fig. 5) carried by the tool are placed across the diagonal to position the tool to achieve correct insertion of the cluster. Engage the holes to join them.

The legs 39 are interconnected in close proximity to the top by a rigidly welded plate 38, which also serves to receive movable grippers of the fuel rod treatment tool. The legs 39 are also connected together in their middle part by means of adapter plates 40. With the corresponding arrangement of the control rods 12 in the cluster 10, the plate 26 is provided with twenty-four holes 38 (FIGS. 5 and 7).

The lower portion of the support 30 defines the inspection area. This area is equipped with means for inspecting vortex currents and is open towards the table for access to ultrasonic and visual inspection means.

The vortex current inspection means is supported by a pedestal 44 with transverse holes having a distribution corresponding to ten rods in the cluster. A vortex current coil 46 is installed above these six holes, each of which surrounds a path of one of the rods. They are combined with circuitry that can function for complete measurements. One ring 48 is coupled on each end of each coil to facilitate centering of each rod.

As shown, only six coils are provided in an attempt to minimize volume. However, other numbers of coils may be provided, for example twelve coils. If you want to perform the test in a single step, you can have the same number of coils as the number of control rods in the cluster.

The coils 46 typically have an analog signal indicating the projection of the measurement signal in two mutually orthogonal directions in the cross section of the control rod and oscillator rack 60 providing an electrical signal at a selected frequency for vortex current inspection. It is coupled with a data processing facility that includes a signal processing rack 61 for transmitting. The signals from the six coils are processed separately by the computer 63, and the results can be displayed on a print out or data plotter 64 (FIG. 4).

In order to compensate for the environment, in particular temperature variations and the impedance of the cable, it will always be desirable to perform differential measurements. To this end, each of the coils 46 may be combined with a reference coil (not shown) which is the same as the first coil and surrounds a portion of the new control rod and is installed close to the first coil.

[Position setting table]

Now, the positioning table 50 shown as an example in FIGS. 5, 6 and 7 will be described. The table is designed for normal adjustment of the position of the optical test camera 42 and the ultrasonic sensor (not shown). As shown, the table 50 consists of a horizontal plate secured to the two legs 39, for example by an angle bracket 52 and a screw 54. Openings 56 formed in the two legs 39 that accept the angle brackets provide access to the inspection area from above the table 50. Six slots 58 are formed on the top of the table and can hold the camera in six different positions, each of which allows for testing of a control rod placed in a different hole 43 (FIG. 7). Are locations.

[Body]

Referring to FIG. 5, the body 32 of the device consists of four square irons 66 joined together by regularly spaced crossbars. In FIG. 5, an upper rung 68a and an intermediate rung 68b are shown, and in FIG. 10, an upper rung 68a and a lower rung 68c are shown. The legs 39 of the support 30 are welded onto the upper rung 68a. Both crossbars are formed with aligned holes 70, the distribution of which corresponds to the arrangement of control rods in the cluster. The guide tubes 72 are accommodated in the holes 70, and each of the guide tubes 72 has a diameter enough to slidably receive the control rod. The crossbar and the iron can be interconnected by any suitable form of means such as, for example, screws, as shown in FIG.

[Spacer Block]

The function of the spacer block 34 is to hold the device in the fuel assembly reservoir at a level above the reservoir of the table. Multiple blocks at other heights may be provided. Each block will have the general configuration shown in FIGS. 8 and 9, similar to that of the body. The block 34 has four vertical corners 74 secured to the crossbar 78 by screws 76 (or any other means), each of which crossbar 78 being distributed according to the control rod arrangement in the control rod cluster. 24 holes are formed. Means may be provided for securing the spacer block 34 on the body 32. As shown in FIG. 8, it consists of a screw 80 coupled to the spiral holes in the lower crosspiece 68c of the body 32.

[Startup Inspection Unit]

6, 7, 11 and 12 show a visual inspection unit having a camera 42 coupled with a mirror holder as a sensor element. The housing of the camera 42 is fixed by two yokes 84 welded to the pedestal 86, the angular position of the pedestal 86 relative to one of the retaining slots 58 of the table 50 being the pedestal. This is ensured by two indexing lugs 88 that are tightly fitted to 86. The winged screw 90 can secure the pedestal 86 on the table 50.

7, 11 and 12, the mirror holder 92 is made of two arrow strips 94. Each strip is formed with a hole 96 for the control rod to be inspected. The bottom edge of the strip 94 is welded to the fixing collar 98 to attach the mirror holder to the body of the camera. At the end of the strip 94 are placed two mirrors 100 at an angle of 120 ° C. which are held in place by a rod 102 which receives the screw 104 helically. Rather than looking at the front of the control rods, the mirrors allow the camera 42 to see the back of the control rod during inspection if it is focused on the image provided by the mirror.

[Ultrasonic Inspection Unit]

Referring to FIG. 13, the ultrasonic inspection unit (rather than manually controlled) is mounted on a remotely controlled table. However, a table as shown in FIG. 6 is also possible.

The ultrasonic inspection unit 106 will be considered to have a control block and an inspection block.

The control or drive block is designed to be fixed on the table. The block has a fluid sealing casing 110 that includes an electric motor 108 (generally a DC motor) coupled to the table by a rectangular bracket 112 and coupled with an angle encoder 114. The output shaft of the motor 108 is fitted to the flexible coupling 116, and the fluid sealing casing 110 has a horizontal guide column 118 parallel to the output shaft.

The inspection block is coupled to the control block to accommodate the deformation of the control rod 12 to be inspected. The inspection block has a support 120, which is connected to the control block by coupling the guide pillar 118 into the guide member 122 belonging to the support 120. Guide pillar 118 allows the support to make small amplitude displacements in rotation and linearly along the pillar. This allows the inspection block to adapt to any defects on the straight line of the control rod 12.

The bottom and top plate of the support 120 are formed with openings provided with roller bearings 124 that rotatably receive a unit 126 that surrounds the position of the control rod 12 to be inspected. The unit 126 is composed of a rotatable sleeve, on which a centralized ultrasonic transducer sensor 128 is mounted. As shown, the sensor is parallel to the vertical axis of rotation of the unit 126. The transmitted and received ultrasonic beams are reflected by the inclined mirror 130. The electrical supply to the sensor and the transmission of the signal are via a rotating electrical contact 136.

The unit 126 is rotatably pulled by a mechanism capable of inspecting the entire outer circumference of the control rod with the sensor 128. As shown, the drive mechanism includes a transmission shaft 138 that rotates in a bearing carried by the top plate of the support 120. The transmission shaft is connected to the output shaft of the motor 108 by a flexible coupling 116 which supports mutual misalignment of the motor shaft and the transmission shaft. The transmission shaft 138 has an end level gear 140 for engaging the level gear 142 carried by the unit 126 which is a sleeve element.

The ultrasonic inspection unit shown in FIG. 13 further includes an apparatus for positioning the control rod 12 relative to the sensor 128. This positioning device includes a flexible centering tool carried by the bottom plate of the support 120. The centering tool has a yoke 144 secured to the support and slidingly receiving the bar 146 to move towards and away from the control rod. The bar 146 carries a carriage 148 to rotatably receive the movable roller 150 having a shape suitable for the shape of the control rod. The second roller 152 is mounted on the shaft carried by the yoke 144 and can slide in the slot 156 in the carry 148. The return spring 158 biases the carriage 148 in the same direction as the movable roller 150 forcing the control rod 12 against the roller 152. Due to this arrangement, the control rod will be centered relative to the ultrasonic sensor 128 while some deformation is compensated for by the sliding motion of the carriage 148.

As described above, the manual adjustment table for the camera can be replaced by a remote control control step for carrying the camera or the ultrasonic inspection unit in a fixed position.

The remotely controlled table shown by way of example in FIG. 13 makes it possible to set the video inspection camera or the ultrasonic sensor 128 at any of the six positions corresponding to the six control rods to be inspected. It is advantageously different from that coupled to the vortex current coil.

The cable shown in FIG. 13 has a cross motion table for moving in two horizontal directions (x, y). The displacement of the table within a defined range is controlled via the trunk connection link system. A connecting link 160 with a trunk (not shown) that can be driven manually or by a motor (not shown) over the pool supports the shaft 162 to which the positioning roller 164 is fixed. During the longitudinal and rotational movement of the connecting link 160 caused by the crank (not shown), the roller 164 moves along the contour of the cam 166 provided in the plate and drives the tool carrier plate 168. Do it. The cross motion table has a first axis 170 parallel to the x direction and a second axis 172 parallel to the y direction, allowing displacement of the bracket 112.

Hereinafter, the operation by the above-described configuration is as follows.

During the first step, the control rod clusters are lowered into the device and the six rods of the cluster are simultaneously examined by the vortex current inspection unit. The test can be performed during the descent and the next upstroke, and the results are recorded. Once a group is lifted to its original position, the same operation is repeated at three different angular positions, namely 90, 180 and 270, respectively, relative to the original position. Next, an image of the total wear of each of the control rods in the cluster is obtained, and it is possible to detect an image of the control rods with wear that should be inspected at least locally more accurately (especially wear due to material loss from the sheath). .

In addition, the inspection is performed by ultrasound or optically, while a second step, which can be performed simultaneously with the first working step, occurs on another rod of the same cluster.

Ultrasonic examinations are generally sufficient to be performed on one control rod at a time because there is no need to perform a systematic check on all control rods over their entire length. In order to perform the ultrasonic inspection, the ultrasonic sensor rotates around the control rod at the same time as the control rod is moved in the axial direction. Typically, points that are distributed every 3 ° with a rotational speed of about 60 rpm are written.

Finally, a visual test is performed with a TV camera that may be replaced by an endoscope if no recording is necessary. During the lower (or upward) motion of the control rods, the camera focuses on the front side of the control rods to be inspected, making it possible to visually detect cracks or tears or to detect loss of end plugs. During the ascending (or falling) movement, the camera focuses on the image through the mirror 100, allowing the complete image of the control rod to be within the critical region. The camera or ultrasonic inspection unit may be placed on the table within the range of the remotely controlled processing tool of the table, with the device being raised (if using a table as shown in FIG. 6) and then appropriate for the control rod to be inspected. The position is set, and the position setting can be done by electric control in the case of the table as shown in FIG.

The present invention can be applied to whatever the number of control rods in a cluster and the characteristics of the control rods, including, for example, contain a nucleophilic material used to change the energy spectrum of neutrons in the reactor.

Claims (6)

A method of inspecting elongated control rods of n parallel control rod clusters that are capable of moving into and out of a reactor core, the method comprising: (a) the total for n / m control rods (m being a predetermined integer less than n); While performing the vortex current checker over the length, move the control rod cluster in the longitudinal direction to pass through the control unit, and (b) after step (a) the cluster has been rotated by a continuous amount of 360 ° / m around the longitudinal direction Repeat m-1 times, and (c) over the entire axial length of the suspicious area and multiple lengths to provide a detailed context of the suspicious area with the suspicious control rods presented during steps (a) and (b). Which consists of the steps of ultrasonically inspecting one during the longitudinal motion of each suspicious control rod in turn along the directional contour. Checking method of control rod clusters for fuel assemblies according to. A device for inspecting a control rod of a control rod cluster capable of vertical movement into and out of the core of a nuclear reactor, said apparatus comprising: a support plate having passageways for the control rod to cross during a sliding movement, and m different numbers of fixed rods around the vertical axis fixed to the support plate; Guide means arranged to slidably receive the control rods of the cluster in cluster positions at an angle, each of which is arranged such that the control rods are traversed during sliding movement along the guide means, where n is the total number of control rods in the cluster and m At least one control rod at a time during a vertical sliding movement of the control rod, comprising n / m vortex current coils in multiples of, a data processor means arranged to receive detection signals from the coil, and at least one ultrasonic and visual inspection means. As a means of inspecting Of the control rod cluster testing apparatus for fuel assembly, characterized in that. 3. The vortex current coil of claim 2, wherein each vortex current coil is connected in a different arrangement with the second coil surrounding the new control rod and arranged to provide a signal dependent on the wear condition at the cross section of the control rod tested with reference to the new portion. In this way, the control device for the control rod cluster for nuclear fuel assembly, characterized in that for compensation for environmental impact. 3. The fuel assembly of claim 2, wherein a device is provided for receiving the group in m = 4 different angular positions for testing the groups used for the fuel assembly in which the control rod is distributed in a rectangular arrangement. Inspection device of control rod cluster. 3. The inspection means according to claim 2, wherein the inspection means comprises an ultrasonic concentrator sensor mounted on the movable element mounted to the support plate for rotating the control rod, and means for rotating the movable element around the control rod to be inspected to obtain a complete indication of the control rod. Inspection device for the control rod cluster for a fuel assembly comprising a. 6. The method of claim 5, wherein the sensor has a sensing axis parallel to the axis of the control rod, and wherein the inspection means further comprises means for directing the transmitted ultrasonic beam towards the control rod and the reflected ultrasonic beam towards the sensor. An apparatus for inspecting a control rod cluster for a nuclear fuel assembly.

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